Warping plywood,


Hello everyone
I am a new homeowner in this 35 yr old townhouse. The roof was redone about 5 yrs ago.
Standing outside and looking at the roof I could see buckling shingles. I thought it was just nails that had pooped, no worries.
But after getting up the attic I could see what was going on and it wasn’t just roofing nail pops.
Who ever installed the plywood had totally missed nailing the edge of plywood to the truss, thus the bow.
Any advice how I can fix this with out removing shingles?
My thought was to sister a 2x to truss from attic and drive screws or ledger-locs from roof to nail the bow down. My only worry is that even if I seal screw heads with roof sealant roof might leak.
Any advice is appreciated as I’m not a roofer.
New user and only can post 1 pic but have more

The only way to do that right is to remove the shingles. Replace some wood and cut back the other sheet a little. Any other way and you will regret it. Pick a warm day and it will be easier.

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You might not need to replace any wood but you will want to add a block to that rafter so you can nail the sheet properly.
Looks like they didn’t centre the sheets properly on the rafters.

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If I sister a 2x4 block to rafter and nail the plywood from above through shingles; will that leak?
I will seal the nail head obviously but just wondered

You will need to remove and reinstall some shingles. You don’t want to just nail through them.

You should be able to unseal and lift the lower portion of the shingles up enough to nail underneath them. Get a tube of asphalt cement to re-seal them.

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